Dimmer

ABSTRACT

A bidirectional switch switched to conduct and interrupt a bidirectional current between a pair of input terminals. An input device receives a dimming level representing a value of light output of the load. A controller controls the bidirectional switch according to the dimming level. The controller controls the bidirectional switch to keep the bidirectional switch in an off-state from a start point of a half cycle of the AC voltage of the AC power supply to a first time point when a first time period therefrom elapses, and to turn the bidirectional switch to an on-state at the first time point. The controller turns the bidirectional switch to the off-state at a second time point when a second time period elapses from the first time point. The controller keeps the bidirectional switch in the off-state from the second time point to an end point of the half cycle.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.16/194,350, which is a Continuation of U.S. patent application Ser. No.15/580,027, which is based on International Application No.PCT/JP2016/002605, which in turn claims priority of Japanese PatentApplication No. 2015-116179, the entire contents of each of which arehereby incorporated by reference.

TECHNICAL FIELD

The invention relates to a dimmer configured to adjust the light outputof a lighting load.

BACKGROUND ART

In a related dimmer, it has been known to adjust the light output of alighting load (for example, Patent Literature 1).

A dimmer described in Patent Literature 1 includes a pair of terminals,a control circuit, a control power supply that is configured to supplythe control circuit with control power, and a dimming operation devicethat is configured to set a dimming level of a lighting load.

The control circuit and the control power supply are connected inparallel between the pair of terminals. A series circuit of an AC powersupply and the lighting load is to be connected between the pair ofterminals. The lighting load includes a plurality of LED (Light EmittingDiode) devices, and a power supply circuit that is configured to lighteach LED device. The power supply circuit includes a smoothing circuitof a diode and an electrolytic capacitor.

The control circuit includes a switch that is configured to performphase control of AC voltage to be supplied to the lighting load, aswitch driver that is configured to drive the switch, and a controllerthat is configured to control the switch driver and the control powersupply.

The control power supply is connected in parallel with the switch. Thecontrol power supply converts the AC voltage of the AC power supply intothe control power. The control power supply includes an electrolyticcapacitor that is configured to store the control power.

The controller is supplied with the control power through theelectrolytic capacitor from the control power supply. The controllerincludes a microcomputer. The microcomputer is configured to performreverse phase control by interrupting the supply of electric power tothe lighting load at an intermediate time point in each half cycle of ACvoltage.

CITATION LIST Patent Literature

Patent Literature 1: JP 2013-149498 A

SUMMARY OF INVENTION

It is an object of the present invention to provide a dimmer compatiblewith more kinds of loads.

A dimmer according to a first aspect of the present invention includes apair of input terminals, a bidirectional switch, a phase detector, aninput device, a power supply and a controller. The pair of inputterminals is configured to be electrically connected between a loadconfigured to be lit when it is energized, and an AC power supply. Thebidirectional switch is configured to be switched so as to conduct andinterrupt a bidirectional current between the pair of input terminals.The phase detector is configured to detect a phase of AC voltage of theAC power supply. The input device is configured to receive a dimminglevel representing a value of light output of the load. The power supplyis electrically connected between the pair of input terminals andconfigured to receive electric power from the AC power supply to producecontrol power. The controller is configured to receive the control powerfrom the power supply to be activated. The controller is configured tocontrol the bidirectional switch based on a detection signal from thephase detector so that the bidirectional switch is in an off-state froma start point of a half cycle of the AC voltage to a first time pointwhen first time therefrom elapses, the bidirectional switch is in anon-state from the first time point to a second time point when secondtime therefrom according to the dimming level elapses, and thebidirectional switch is in an off-state from the second time point to anend point of the half cycle.

A dimmer according to a second aspect of the present invention includesa bidirectional switch, a phase detector, a power supply and acontroller. The bidirectional switch is configured to be connected to anAC power supply with the bidirectional switch connected in series to aload, and configured to perform phase control of AC voltage of the ACpower supply to be supplied to the load. The phase detector isconfigured to detect a phase of the AC voltage of the AC power supply.The power supply is connected in parallel with the bidirectional switch,and configured to perform conversion operation to convert the AC powersupply into prescribed control power. The power supply has a capacitivedevice configured to store the control power. The controller isconfigured to receive the control power through the capacitive devicefrom the power supply. The controller is configured to divide each halfcycle of the AC voltage into a first time period, a second time period,a third time period and a fourth time period based on the phase detectedwith the phase detector. The controller is also configured to, duringthe first and fourth time periods, modulate the bidirectional switch outof conduction to interrupt supply of electric power to the load, andcause the power supply to perform the conversion operation. Thecontroller is also configured to, during the second time period,modulate the bidirectional switch into conduction to supply electricpower to the load, and stop the power supply performing the conversionoperation. The controller is also configured to, during the third timeperiod, modulate the bidirectional switch out of conduction to interruptthe supply of electric power to the load.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic circuit diagram showing a configuration of adimmer according to Embodiment 1;

FIG. 2 is a timing chart showing an operation of the dimmer according toEmbodiment 1;

FIG. 3 is a timing chart used for comparing the dimmer according toEmbodiment 1 and a comparison example;

FIG. 4 is a schematic circuit diagram showing a configuration of adimmer as Modified Example 1 of Embodiment 1;

FIG. 5 is a schematic circuit diagram showing a configuration of adimmer as Modified Example 2 of Embodiment 1;

FIG. 6 is a timing chart showing an operation of the dimmer as ModifiedExample 2 of Embodiment 1; and

FIG. 7 is a schematic circuit diagram showing a configuration of adimmer according to Embodiment 2.

DESCRIPTION OF EMBODIMENTS Embodiment 1 (1.1) Configuration

A dimmer 1 according to the present embodiment will hereinafter beexplained. Note that the configuration to be explained below is merelyone example of the present invention, and the present invention is notlimited by the embodiment described below, but various modifications maybe made therein according to design and the like as long as they areeven modifications other than the embodiment and fall within the scopeof technical ideas of the present invention. As shown in FIG. 1, thedimmer 1 according to the present embodiment includes a pair of inputterminals 11 and 12, a bidirectional switch 2, a phase detector 3, aninput device 4, a power supply 5, a controller 6, a switch driver 9,diodes D1 and D2, and a stopper 13.

The pair of input terminals 11 and 12 is configured to be electricallyconnected between a load 7 configured to be lit when it is energized,and an AC power supply 8. The bidirectional switch 2 is configured to beswitched so as to conduct and interrupt (cut off) a bidirectionalcurrent between the pair of input terminals 11 and 12. The phasedetector 3 is configured to detect a phase of AC voltage Vac of the ACpower supply 8. The input device 4 is configured to receive a dimminglevel representing a value of light output of the load 7. The powersupply 5 is electrically connected between the pair of input terminals11 and 12, and is configured to receive electric power from the AC powersupply 8 to produce control power.

The controller 6 is configured to receive the control power suppliedfrom the power supply 5 to be activated. The controller 6 is configuredto control the bidirectional switch 2 based on a detection signal fromthe phase detector 3 so that the bidirectional switch 2 is in anoff-state from a start point of a half cycle of the AC voltage Vac to afirst time point when first time therefrom elapses, the bidirectionalswitch 2 is in an on-state from the first time point to a second timepoint when second time therefrom according to the dimming level elapses,and the bidirectional switch 2 is in an off-state from the second timepoint to an end time point of the half cycle.

Here, the expression of “from a time point A” means that the time pointA is included. For example, “from the first time point” means that thefirst time point is included. On the other hand, the expression of “to atime point A” means just before the time point A and the time point A isnot included. For example, “to a first time point” means just before thefirst time point and the first time point is not included. Moreover, the“input terminals” may be, for example, leads of electronic components orpart of conductor included in a circuit board, and needn't have entityas parts (terminals) to be connected with electric wires or the like.

The dimmer 1 is a two-wire type of dimmer, and used so that the dimmer 1is connected to the AC power supply 8 with the dimmer 1 electricallyconnected in series to the load 7. The load 7 is lit when it isenergized. The load 7 includes (an) LED devices as a light source, and alighting circuit configured to light the LED devices. The AC powersupply 8 is, for example a 100 [V] 60 [Hz] single phase commercial powersupply. The dimmer 1 is applicable to a wall switch as one example orthe like.

The bidirectional switch 2 is composed of, for example, two devices suchas first and second switch devices Q1 and Q2 that are electricallyconnected in series between the pair of input terminals 11 and 12. Forexample, each of the first and second switch devices Q1 and Q2 is asemiconductor switch device such as an n-channel enhancement MOSFET(Metal-Oxide-Semiconductor Field Effect Transistor).

The switch devices Q1 and Q2 are anti-series connected between the pairof input terminals 11 and 12. That is, the switch devices Q1 and Q2 haverespective sources that are connected to each other. The switch deviceQ1 has a drain that is connected to the input terminal 11, and theswitch device Q2 has a drain that is connected to the input terminal 12.The sources of the switch devices Q1 and Q2 are connected to ground(earth) of the power supply 5. The ground (earth) of the power supply 5functions as reference potential of (an) internal circuits of the dimmer1.

The bidirectional switch 2 can switch among four states by combinationsof ON and OFF of the switch devices Q1 and Q2. The four states include abidirectional off-state in which both the switch devices Q1 and Q2 areoff, a bidirectional on-state in which both the switch devices Q1 and Q2are on, and two kinds of unidirectional on-states in each of which onlyone of the switch devices Q1 and Q2 is on. With a unidirectionalon-state, between the pair of input terminals 11 and 12 is formed aunidirectional conduction from a switch device, which is on, of theswitch devices Q1 and Q2 through a body diode of a switch device, whichis off, of the switch devices Q1 and Q2. For example, when the switchdevices Q1 and Q2 are on and off, respectively, a first unidirectionalon-state is formed so as to allow an electric current to flow from theinput terminal 11 to the input terminal 12. When the switch devices Q1and Q2 are off and on, respectively, a second unidirectional on-state isformed so as to allow an electric current to flow from the inputterminal 12 to the input terminal 11. Therefore, when the AC voltage Vacis applied between the input terminals 11 and 12 from the AC powersupply 8, the first unidirectional on-state and the secondunidirectional on-state are a “forward on-state” and a “reverseon-state”, respectively, during positive AC voltage Vac, namely during apositive half cycle on a side of the input terminal 11. On the otherhand, during negative AC voltage Vac, namely during a positive halfcycle on a side of the input terminal 12, the first unidirectionalon-state and the second unidirectional on-state are “reverse on-state”and “forward on-state”, respectively.

Here, the bidirectional switch 2 is in an on-state in the case of boththe “bidirectional on-state” and the “forward on-state”, and is in anoff-state in the case of both the “bidirectional off-state” and the“reverse on-state”.

The phase detector 3 is configured to detect a phase of the AC voltageVac applied between the input terminals 11 and 12. Herein, examples ofthe “phase” include a zero cross point of the AC voltage Vac, andrespective polarity of the AC voltage Vac (positive polarity andnegative polarity). The phase detector 3 is configured to provide thecontroller 6 with a detection signal when detecting a zero cross pointof the AC voltage Vac. The phase detector 3 has a diode D31, a firstdetector 31, a diode D32 and a second detector 32. The first detector 31is electrically connected to the input terminal 11 via the diode D31.The second detector 32 is electrically connected to the input terminal12 via the diode D32. The first detector 31 is configured to detect azero cross point when the AC voltage Vac shifts from a negative halfcycle to a positive half cycle. The second detector 32 is configured todetect a zero cross point when the AC voltage Vac shifts from a positivehalf cycle to a negative half cycle.

That is, the first detector 31 detects a zero cross point when detectingthat positive voltage on the input terminal 11 shifts from a state lessthan a specified value to a state greater than or equal to the specifiedvalue. Similarly, the second detector 32 detects a zero cross point whendetecting that positive voltage on the input terminal 12 shifts from astate less than a specified value to a state greater than or equal tothe specified value. The specified values are values (absolute values)that are set to approximately 0 [V]. For example, the specified value ofthe first detector 31 is about positive several volts, and the specifiedvalue of the second detector 32 is about negative several volts.Strictly speaking, a detection time point of the zero cross pointdetected with the first and second detectors 31 and 32 is slightlydelayed from the zero cross point (0 [V]).

The input device 4 is configured to receive a signal representing adimming level from an operation device to be operated by a user toprovide the controller 6 with the signal as a dimming signal. Beforeoutputting the dimming signal, the input device 4 may process the signalreceived, or may omit to process it. The dimming signal is a numericalvalue or the like representing a value of light output from the load 7,and may include an “OFF level” that forces the load 7 to be unlit. Theoperation device needs to be configured to receive user's operation toprovide the input device 4 with a signal representing a dimming level,and examples thereof include a variable resistor, a rotary switch, atouch panel, a remote controller, a communication terminal such as asmartphone, and the like.

The controller 6 is configured to control the bidirectional switch 2based on the detection signal from the phase detector 3 and the dimmingsignal from the input device 4. The controller 6 is configured toindividually control the switch devices Q1 and Q2. Specifically, thecontroller 6 is to control the switch device Q1 according to a firstcontrol signal and control the switch device Q2 according to a secondcontrol signal.

For example, the controller 6 is mainly composed of a microcomputer. Themicrocomputer includes a CPU (Central Processing Unit) that executes aprogram stored in a memory of the microcomputer, thereby functioning asthe controller 6. The program may be stored in the memory of themicrocomputer in advance, provided through a storage medium such as amemory card, or provided through a telecommunications line. In otherwords, the program is provided for causing a computer (here,microcomputer) to function as the controller 6.

The switch driver 9 has a first driver 91 configured to drive (performOn and Off control of) the switch device Q1, and a second driver 92configured to drive (perform On and Off control of) the switch deviceQ2. The first driver 91 is configured to receive the first controlsignal from the controller 6 to apply gate voltage to the switch deviceQ1. The first driver 91 accordingly performs the On and Off control ofthe switch device Q1. Similarly, the second driver 92 is configured toreceive the second control signal from the controller 6 to apply gatevoltage to the switch device Q2. The second driver 92 accordinglyperforms the On and Off control of the switch device Q2. The firstdriver 91 is configured to produce the gate voltage on the basis ofsource potential of the switch device Q1. The second driver 92 issimilar thereto.

The power supply 5 has a control power supply 51 configured to producecontrol power, a driving power supply 52 configured to produce drivingpower, and a capacitive device (capacitor) C1. The control power ispower for activating the controller 6. The driving power is power fordriving the switch driver 9. The capacitive device C1 is electricallyconnected to an output terminal of the control power supply 51, and isto be charged by an output current of the control power supply 51.

The power supply 5 is electrically connected to the input terminal 11through the diode D1, and electrically connected to the input terminal12 through the diode D2. The AC voltage Vac applied between the inputterminals 11 and 12 is accordingly supplied to the power supply 5 afterbeing full-wave rectified by a diode bridge that is composed of the pairof diodes D1 and D2 and respective body diodes of the switch devices Q1and Q2. The driving power supply 52 smooths the AC voltage Vac full-waverectified to produce the driving power. The driving power supply 52supplies the driving power to the switch driver 9 and the control powersupply 51. The driving power has, for example the voltage of 10 [V]. Thecontrol power supply 51 steps down the driving power supplied from thedriving power supply 52 to produce the control power, providing thecontrol power to the capacitive device C1. The control power has, forexample the voltage of 3 [V]. The control power supply 51 may directlyproduce the control power from the AC voltage Vac full-wave rectified,not through the driving power supply 52. In short, the power supply 5 isconfigured to receive electric power from the AC power supply 8 toproduce the control power and the driving power.

The stopper 13 is configured to stop the power supply 5 producing thecontrol power during a stop time period. In the present embodiment, thestopper 13 stops the power supply 5 producing the control power byelectrically disconnecting the power supply 5 or controlling asemiconductor switch device included in the power supply 5. In theexample of FIG. 1, the stopper 13 forms a series circuit along with thepower supply 5, and the series circuit of the stopper 13 and the powersupply 5 is electrically connected in parallel with the bidirectionalswitch 2 between the pair of input terminals 11 and 12. Although thestop time period will be explained in “(1.2.2) Dimming operation” indetail, the stop time period is a period of time from which at least aperiod of time during which the bidirectional switch 2 is in thebidirectional off-state is excluded. Specifically, the stopper 13 is aswitch that is electrically connected between a junction of the pair ofdiodes D1 and D2 and the power supply 5, and configured to turn off whenreceiving a disconnection signal from the controller 6 and disconnectthe power supply 5 from the input terminals 11 and 12.

The dimmer 1 according to the present embodiment includes a maskprocessor 61. The mask processor 61 is configured to, when receiving adetection signal from the phase detector 3, disable the detection signalover a constant length of mask time. In the embodiment, the controller 6is integrally provided with the mask processor 61 as one function of thecontroller 6. Although the mask processor 61 will be explained in“(1.2.2) Dimming operation” in detail, the mask processor 61 disablesthe detection signal from the phase detector 3 during the mask time, andthereby the controller 6 hardly receives the influence of errors indetection of the zero cross point by the phase detector 3. Preferably,the mask processor 61 individually disables respective detection signalsof the first and second detectors 31 and 32.

The lighting circuit of the load 7 is configured to read a dimming levelfrom a waveform of the AC voltage Vac phase-controlled with the dimmer 1and vary a value of the light output of the LED devices. Here, as anexample, the lighting circuit has a circuit for securing an electriccurrent such as a bleeder circuit. The lighting circuit thereforeenables an electric current to flow through the load 7 even when thebidirectional switch 2 of the dimmer 1 does not conduct.

(1.2) Operation (1.2.1) Activation Operation

First, an activation operation of the dimmer 1 according to the presentembodiment when it is initially energized will be explained.

With the dimmer 1 configured as stated above, when the AC power supply 8is connected between the input terminals 11 and 12 through the load 7,the AC voltage Vac applied between the input terminals 11 and 12 fromthe AC power supply 8 is rectified and then supplied to the drivingpower supply 52. Driving power is produced through the driving powersupply 52 and supplied to the switch driver 9 and the control powersupply 51. Control power is produced through the control power supply 51and supplied to the controller 6, and thereby the controller 6 isactivated.

When the controller 6 is activated, the controller 6 judges a frequencyof the AC power supply 8 based on detection signals from the phasedetector 3. The controller 6 then refers to a numerical value table thatis stored in the memory in advance according to the frequency judged,and performs the setting of parameters for various kinds of time (forexample, mask time and stop time period to be described later). Here,when a dimming level received through the input device 4 is an “OFFlevel”, the controller 6 keeps a bidirectional off-state of thebidirectional switch 2, thereby keeping a high impedance state of theimpedance between the pair of input terminals 11 and 12. The load 7accordingly keeps an unlit state.

(1.2.2) Dimming Operation

The dimming operation of the dimmer 1 according to the presentembodiment will next be explained with reference to FIG. 2. FIG. 2depicts the AC voltage “Vac”, the first detection signal “ZC1”, firstmask processing “MASK 1”, the second detection signal “ZC2”, second maskprocessing “MASK2”, the first control signal “Sb1”, the second controlsignal “Sb2”, and the disconnection signal “Ss1”. Here, the firstdetection signal ZC1 is a detection signal by the first detector 31, andthe second detection signal ZC2 is a detection signal by the seconddetector 32. The first mask processing MASK 1 is mask processing(disabling processing) of the first detection signal ZC1 through themask processor 61, and the second mask processing MASK 2 is maskprocessing of the second detection signal ZC2 through the mask processor61. Herein, the first detection signal ZC1 changing from an “H” level toan “L” level is regarded as the first detection signal ZC1 beinggenerated. In addition, the second detection signal ZC2 changing from an“H” level to an “L” level is regarded as the second detection signal ZC2being generated. That is, each of the first and second detection signalsZC1 and ZC2 is a signal that changes from an “H” level to an “L” levelwhen a zero cross point is detected.

First, an operation of the dimmer 1 during a positive half cycle of theAC voltage Vac will be explained. The dimmer 1 detects a zero crosspoint of the AC voltage Vac as a standard of the phase control throughthe phase detector 3. When the AC voltage Vac shifts from a negativehalf cycle to a positive half cycle to reach the specified value “Vzc”,the first detector 31 outputs a first detection signal ZC1. Whenreceiving the first detection signal ZC1, the controller 6 outputs firstand second control signals Sb1 and Sb2 each of which is an “OFF” signal.

Both the switch devices Q1 and A2 are accordingly off and thebidirectional switch 2 is in a bidirectional off-state, during a firsttime period T1 from a start point of the half cycle (zero cross point)t0 to a first time point t1 when first time therefrom elapses. In thepresent embodiment, a point in time when the first detection signal ZC1is generated is regarded as a “detection point”, and a sum of a periodof time from the start point of the half cycle (zero cross point) t0 tothe detection point and a period of time from the detection point to apoint in time when a constant time (e.g., 300 [μs]) therefrom elapses isregarded as the first time period T1. That is, in the embodiment, thecontroller 6 controls to cause the bidirectional switch 2 to be in abidirectional off-state not only on and after the detection point butalso during the period of time from the start point of the half cycle(zero cross point) t0 to the detection point. Here, if the AC voltageVac has a constant frequency, each period of time from a start point ofthe half cycle (zero cross point) t0 to a detection point is a constantlength of time, and therefore the first time (period of time from startpoint of half cycle, t0, to first time point t1) is a constant length oftime.

At the point in time when the constant time (e.g., 300 [μs]) elapsesfrom the detection point, namely the first time point t1, the controller6 outputs the first and second control signals Sb1 and Sb2 each of whichis an “ON” signal.

A second time point t2 is a point in time at which second time from thefirst time point t1 according to a dimming signal elapses. At the secondtime point t2, the controller 6 changes the first control signal Sb1 toan “OFF” signal while keeping the second control signal Sb2 that is the“ON” signal. During a second time period T2 from the first time point t1to the second time point t2, both the switch devices Q1 and Q2 are onand the bidirectional switch 2 is in a bidirectional on-state. The load7 is therefore supplied with electric power through the bidirectionalswitch 2 from the AC power supply 8 to be lit.

A third time point t3 is a point in time that is earlier by a constanttime (e.g., 300 [μs]) than an end point of the half cycle (zero crosspoint) t4. At the third time point t3, the controller 6 causes both thefirst and second control signals Sb1 and Sb2 to be “OFF” signals.Accordingly, during a third time period T3 from the second time point t2to the third time point t3, only the switch device Q1 of the switchdevices Q1 and Q2 is off and the bidirectional switch 2 is in a reverseon-state (i.e., in OFF state). Electric power from the AC power supply 8to the load 7 is cut off during the third time period T3.

During a fourth time period T4 from the third time point t3 to the endpoint of the half cycle (zero cross point) t4, both the switch devicesQ1 and Q2 are off and the bidirectional switch 2 is in a bidirectionaloff-state.

An operation of the dimmer 1 during a negative half cycle of the ACvoltage Vac is basically similar to the operation of the positive halfcycle.

In the negative half cycle, a period of time from a start point of thehalf cycle (zero cross point) t0 (t4) to a first time point t1 whenfirst time therefrom elapses is regarded as a first time period T1. Inthe present embodiment, a point in time when a second detection signalZC2 is generated is regarded as a “detection point”, and a sum of aperiod of time from the start point of the half cycle (zero cross point)t0 (t4) to the detection point and a period of time from the detectionpoint to a point in time when a constant time (e.g., 300 [μs]) therefromelapses is regarded as the first time period T1. A second time point t2is a point in time when second time from the first time point t1according to the dimming signal elapses. A third time point t3 is apoint in time that is earlier by a constant time (e.g., 300 [μs]) thanan end point of the half cycle (zero cross point) t4 (t0). When the ACvoltage Vac reaches a negative specified value “−Vzc”, the seconddetector 32 outputs the second detection signal ZC2. When receiving thesecond detection signal ZC2, the controller 6 causes the first andsecond control signals Sb1 and Sb2 to be “OFF” signals. Thebidirectional switch 2 is accordingly in a bidirectional off-stateduring the first time period T1. At the first time point t1, thecontroller 6 outputs the first and second control signals Sb1 and Sb2each of which is an “ON” signal.

At the second time point t2, the controller 6 changes the second controlsignal Sb2 to an “OFF” signal while keeping the first control signal Sb1that is the “ON” signal. During a second time period T2 from the firsttime point t1 to the second time point t2, both the switch devices Q1and Q2 are on and the bidirectional switch 2 is in a bidirectionalon-state. The load 7 is therefore supplied with electric power throughthe bidirectional switch 2 from the AC power supply 8 to be lit, duringthe second time period T2.

At the third time point t3, the controller 6 causes the first and secondcontrol signals Sb1 and Sb2 to be “OFF” signals. Accordingly, during athird time period T3 from the second time point t2 to the third timepoint t3, only the switch device Q2 of the switch devices Q1 and Q2 isoff and the bidirectional switch 2 is in a reverse on-state (i.e., inoff state). Electric power from the AC power supply 8 to the load 7 istherefore cut off during the third time period T3.

The dimer 1 according to the present embodiment performs the dimming ofthe load 7 by alternately repeating the operations of the positive andnegative half cycles of the AC voltage Vac as explained above. Thebidirectional switch is in an off state during a period of time from astart point of a half cycle (zero cross point) t0 to a first time pointt1. The bidirectional switch is also in an off state during a period oftime from a second time point t2 to an end point of the half cycle (zerocross point) t4. Therefore, when focusing on two successive half cycles,the bidirectional switch is in an off state from a second time point t2in a first half cycle to a first time point t1 in the next half cycle(i.e., second half cycle).

Here, since the time from the first time point t1 to the second timepoint t2 (second time) is time according to the dimming level receivedthrough the input device 4, time of conduction between the inputterminals 11 and 12 in the half cycle is defined by the dimming level.That is, a short second time makes the light output of the load 7 small,and a long second time makes the light output of the load 7 large. Thedimming level to be received by the input device 4 accordingly enablesvarying the light output of the load 7. Before and after a zero crosspoint of the AC voltage Vac, the bidirectional switch 2 is within aperiod of time (first time period T1 or fourth time period T4) duringwhich the bidirectional switch 2 is in a bidirectional off-state, andthe dimmer 1 can therefore secure the supply of electric power from theAC power supply 8 to the power supply 5 during the period of time. Thepresent embodiment enables securing the supply of electric power fromthe AC power supply 8 to the power supply 5 during at least one of thefirst time period T1 and the fourth time period T4. Note that when auser operates the operation device to adjust the light output of theload 7 to maximum, the second time period T2 may be adjusted to a periodof time that is shorter than a length of time that makes the lightoutput maximum with the first time period T1 and the fourth time periodT4 preferentially secured.

The dimmer 1 according to the present embodiment includes the maskprocessor 61, and is configured to perform mask processing of disablinga detection signal of a zero cross point over a constant length of masktime on and after receiving the detection signal of the zero crosspoint. That is, after receiving a first detection signal ZC1 from thefirst detector 31, the mask processor 61 sets the first mask processingMASK1 to “ON” to disable the first detection signal ZC1 until the masktime elapses. Similarly, after receiving the second detection signal ZC2from the second detector 32, the mask processor 61 sets the second maskprocessing MASK2 to “ON” to disable the second detection signal ZC2until the mask time elapses. The length of the mask time is set on thebasis of the half cycle of the AC voltage Vac. Herein, as an example,the mask time is set to time slightly shorter than twice the length ofthe half cycle (i.e., one cycle). In FIG. 2, the first and seconddetection signals ZC1 and ZC2 disabled are shown by dashed lines.

Once a zero cross point is detected, the mask processing is applied upto the vicinity of a next zero cross point. For example, even when azero cross point is detected in error due to the influence of noise at apoint in time of ¼ cycle from the detection of a zero cross point, adetection signal detected in error is disabled by the mask processing.The controller 6 therefore hardly receives the influence of the zerocross point detected in error by the phase detector 3.

The dimmer 1 according to the present embodiment is configured tocontrol the stopper 13 by the disconnection signal Ss1. During the stoptime period, the stopper 13 electrically disconnects the power supply 5or controls the semiconductor switch included in the power supply 5,thereby stopping the power supply 5 producing the control power. Thatis, during the stop time period, the controller 6 outputs adisconnection signal Ss1 as an “OFF” signal to turn the stopper 13 off,thereby disconnecting the power supply 5 from the input terminals 11 and12. The stop time period is a period of time from which at least aperiod of time during which the bidirectional switch 2 is in abidirectional off-state (first time period T1 or fourth time period T4)is excluded. The stop time period is set in a range of the second timeperiod T2 during which the bidirectional switch 2 is in thebidirectional on-state and the third time period T3 during which thebidirectional switch 2 is in the unidirectional on-state (reverseon-state). Herein, as an example, the stop time period is set so that apoint in time between the first time point t1 and the second time pointt2 is regarded as a start point thereof and the third time point t3 isregarded as an end point thereof. That is, the stop time period is setto be in a period of time having a possibility that electric power willbe supplied from the AC power supply 8 to the load 7.

The dimmer 1 can therefore maintain a high impedance between the inputterminals 11 and 12 by an amount as a result of the disconnection of thepower supply 5 from the input terminals 11 and 12 during the stop timeperiod. That is, the dimmer 1 can supply the power supply 5 withelectric power from the AC power supply 8 for a period of time duringwhich the bidirectional switch 2 is in a bidirectional off-state, andmaintain a high impedance between the input terminals 11 and 12 for aperiod of time during which electric power is not supplied to the powersupply 5 (stop time period). For example, the high impedance between theinput terminals 11 and 12 is maintained for the third time period T3during which the bidirectional switch 2 is in a reverse on-state,thereby preventing electric power caused by a leakage circuit from beingsupplied to the load 7. It is accordingly possible to vary a value oflight output of the load 7 according to a small change of the dimminglevel and improve responsiveness of the load 7.

(1.3) Brief of Dimmer According to Embodiment 1

As explained above, the dimmer 1 according to the present embodimentincludes the bidirectional switch 2, the phase detector 3, the powersupply 5 and the controller 6.

The bidirectional switch 2 is configured to be connected to the AC powersupply 8 with the bidirectional switch 2 connected in series to the load7, and perform the phase control of the AC voltage Vac to be supplied tothe load 7. The phase detector 3 is configured to detect a phase of theAC voltage Vac of the AC power supply 8. The power supply 5 is connectedin parallel with the bidirectional switch 2, and is configured toperform a conversion operation to convert the AC power supply 8 intoprescribed control power. The power supply 5 has the capacitive deviceC1 configured to store the control power.

The controller 6 is configured to be supplied with the control powerthrough the capacitive device C1 from the power supply 5, and divideeach half cycle of the AC voltage Vac into the first time period T1, thesecond time period T2, the third time period T3 and the fourth timeperiod T4. The controller 6 is configured to, during the first andfourth time periods T1 and T4, modulate the bidirectional switch 2 outof conduction to interrupt the supply of electric power to the load 7and cause the power supply 5 to perform the conversion operation. Thecontroller 6 is configured to, during the second time period T2,modulate the bidirectional switch 2 into conduction to supply theelectric power to the load 7 and stop the power supply 5 performing theconversion operation. The controller 6 is configured to, during thethird time period T3, modulate the bidirectional switch 2 out ofconduction to interrupt the supply of electric power to the load 7.

Here, “modulate . . . out of conduction” means causing the bidirectionalswitch 2 to be in an off-state. In addition, “modulate . . . intoconduction” means causing the bidirectional switch 2 to be in anon-state. The “conversion operation” also means an operation forconcerting the AC power supply 8 into the prescribed control power,namely an operation for producing the control power by electric powersupplied from the AC power supply 8.

The dimmer 1 may further include the stopper 13 configured to beswitched to cause the power supply 5 to perform and stop the conversionoperation. In this case, for example, during the third time period T3,the stopper 13 may stop the power supply 5 performing the conversionoperation while the controller 6 modulates the bidirectional switch 2out of conduction to interrupt the supply of electric power to the load7.

(1.4) Comparison with Comparison Example

Hereinafter, a comparison example is based on reverse phase control thatis different from that of the present embodiment. Differencetherebetween in case the control by the present embodiment and thecontrol by the comparison example are compared will be explained withreference to the drawings.

Although the comparison example shown herein is different in controller(6)'s operation (control of bidirectional switch 2) from the presentembodiment, the circuit configuration thereof is the same as that of thepresent embodiment. Therefore, like elements are assigned the samereference numerals as depicted in the present embodiment, and will beexplained. FIG. 3 depicts the AC voltage “Vac”, a first control signal“Sa1” and a second control signal “Sa2” of the comparison example, andthe first control signal “Sb1” and the second control signal “Sb2” ofthe present embodiment.

A dimmer of the comparison example alternately causes the first andsecond control signals Sa1 and Sa2 to be “on” per cycle that is the sameas that of the AC voltage Vac. With the comparison example, abidirectional switch 2 conducts during a period of time during a switchdevice of switch devices Q1 and Q2 on a high potential side of the ACvoltage Vac is turned on. That is, the comparison example performs whatis called reverse control as shown in FIG. 3 where a pair of inputterminals 11 and 12 conducts during a time period Ta1 from a zero crosspoint of the AC voltage Vac to an intermediate point in a half cyclethereof. Therefore, adjusting a phase difference between the first andsecond control signals Sa1 and Sa2 and the AC voltage Vac enablesadjusting conduction time of the bidirectional switch 2.

As compared with the comparison example, the present embodiment hasDifference 1 and Difference 2 below.

[Difference 1]

As shown in [X] of FIG. 3, the present embodiment includes a period oftime during which the bidirectional switch 2 is in a bidirectionalon-state (second time period T2), whereas the comparison example has noperiod of time during which the bidirectional switch 2 is in abidirectional on-state.

That is, in the comparison example, the pair of input terminals 11 and12 conducts as a result of the bidirectional switch 2 being in aunidirectional on-state (forward on-state), whereas in the presentembodiment the pair of input terminals 11 and 12 conducts as a result ofthe bidirectional switch 2 being in a bidirectional on-state. Thus, inthe dimmer 1 according to the embodiment, the bidirectional switch 2 isin a bidirectional on-state while the pair of input terminals 11 and 12conducts, thereby enabling the suppression of a conduction loss by thebidirectional switch 2 in comparison with the comparison example wherethe bidirectional switch 2 is in a unidirectional on-state.

[Difference 2]

As shown in [Y] of FIG. 3, before and after a zero cross point of the ACvoltage Vac, the present embodiment includes a period of time duringwhich the bidirectional switch 2 is in a bidirectional off-state (firsttime period T1 or fourth time period T4), whereas the comparison examplediffers therefrom in that it does not have such a period of time.

That is, with the comparison example, the pair of input terminals 11 and12 conducts during a time period Ta1 from a zero cross point of the ACvoltage Vac to an intermediate point of a half cycle thereof, therebymaking it possible to secure a chance of the supply of electric powerfrom the AC power supply 8 to a power supply 5 only during latter partof the half cycle. There is however a possibility that an electriccurrent will not flow through a load 7 during the latter part of thehalf cycle of the AC voltage Vac depending on a kind of the load 7, suchas a load 7 to which a condenser input type lighting circuit is adopted.There is therefore a possibility that during a period of time duringwhich the pair of input terminals 11 and 12 does not conduct, enoughelectric power to the power supply 5 cannot be secured from the AC powersupply 8 because enough electric current cannot flow through the powersupply 5. The comparison example may consequently be unable to maintainthe supply of control power from the power supply 5 to a controller 6.

In contrast, the dimmer 1 according to the present embodiment causes thebidirectional switch 2 to be in a bidirectional off-state during theperiod of time from the start point of the half cycle (zero cross point)t0 to the first time point t1 (first time period T1), and therefore theperiod of time can be applied to the supply of electric power to thepower supply 5. The dimmer 1 according to the embodiment is providedwith a period of time during which the bidirectional switch 2 does notconduct during former part of the half cycle of the AC voltage Vac(first time period T1), thereby making it possible to secure a chance ofthe supply of electric power from the AC power supply 8 to the powersupply 5 during the former part of the half cycle. The dimmer 1according to the embodiment can therefore maintain the power supply ofelectric power from the AC power supply 8 to the power supply 5 for morekinds of loads 7 in comparison with the comparison example.

The dimmer 1 causes the bidirectional switch 2 to be in a bidirectionaloff-state even during a period of time from the third time point t3 tothe end point of the half cycle t4 (fourth time period T4), andtherefore the period of time can also be applied to the supply ofelectric power to the power supply 5. That is, the dimmer 1 is providedwith the period of time during which the bidirectional switch 2 does notconduct even during the latter part of the half cycle (fourth timeperiod T4), thereby making it possible to secure a chance of the supplyof electric power from the AC power supply 8 to the power supply 5 evenduring the latter part of the half cycle.

(1.5) Advantages

As a control method of the dimmer, there is a positive phase controlmethod (leading edge method) by which the pair of input terminals 11 and12 is to conduct for a period of time from an intermediate point of eachhalf cycle of the AC voltage Vac, besides the revers phase controlmethod (trailing edge method). The revers phase control method is tostart supplying electric power to the load 7 including (an) LED devicesas a light source from each zero cross point, and it is thereforepossible to reduce the distortion of current waveform when startingsupplying the electric power. There are accordingly advantages ofenabling an increase in the number of loads 7 allowed to be connected tothe dimmer and the suppression of the occurrence of beat sound.

Although the dimmer 1 according to the present embodiment is basicallyon the basis of the revers phase control method, the dimmer 1 isprovided with a chance of the supply of electric power from the AC powersupply 8 to the power supply 5 during the former part in each half cycleof the AC voltage Vac. The supply of electric power to the load 7 startsat the first time point t1 when the first time from a zero cross pointelapses, and there is therefore a possibility that the distortion ofcurrent waveform will be larger than that by the reverse phase controlmethod like the abovementioned comparison example. However, theinfluence of the distortion of current waveform is insignificantly smallbecause an absolute value of the AC voltage Vac at the first time pointt1 is not so large. On the other hand, there is an advantage of securingrequisite control power for the operation of the controller 6 andenabling the stable operation.

The dimmer 1 according to the embodiment can reduce errors in detectionby the phase detector 3 by causing the bidirectional switch 2 to be in areverse on-state during a period of time from the second time point t2to the third time point t3 (third time period T3). That is, voltage withpolarity reverse to that of the AC voltage Vac (hereinafter referred toas “reverse polarity voltage”) may be applied between the pair of inputterminals 11 and 12 as a result of an absolute value of voltage acrossthe load 7 exceeding the absolute value of the AC voltage Vac dependingon the load 7. For example, such reverse polarity voltage is liable tooccur in the case of a load 7 that voltage thereacross hardly decreases,such as a load 7 provided with a buffer capacitor having a comparativelylarge capacity. When the reverse polarity voltage occurs, the phasedetector 3 may detect a zero cross point in error at a time point out ofthe zero cross points of the AC voltage Vac. In the case of a load 7where according to the dimming level the reverse polarity voltage mayoccur or not, such a load 7 may have a sudden change in a zero crosspoint when the dimming level is varied. During the third time period T3,the bidirectional switch 2 is in a reverse on-state and therefore theoccurrence of such reverse polarity voltage is suppressed. It istherefore possible to reduce errors in detection by the phase detector3, caused by the reverse polarity voltage. Even during a period of timeduring which the bidirectional switch 2 is in a reverse on-state (thirdtime period T3), the pair of input terminals 11 and 12 does not conduct,thereby enabling the application of the period of time to the supply ofelectric power to the power supply 5 by causing the disconnection signalto be an “ON” signal.

The dimmer 1 enables keeping the supply of electric power from the powersupply 5 to the controller 6, thereby preventing abnormal operationssuch as blinking and flicker of the load 7.

The control of the bidirectional switch 2 according to the embodimentmay be the control to the “forward on-state” instead of the“bidirectional on-state”, or the control to the “bidirectional on-state”instead of the “forward on-state” in contrast. The control may also bethe control to the “reverse on-state” instead of the “bidirectionaloff-state”, or the control to the “bidirectional off-state” instead ofthe “reverse on-state”. That is, an On or Off state of the bidirectionalswitch 2 needs to be unchanged.

As stated in the present embodiment, the bidirectional switch 2 ispreferably configured to be switched to any one of a bidirectionaloff-state in which a bidirectional current between the input terminals11 and 12 is cut off, a bidirectional on-state in which thebidirectional current is conducted, and a unidirectional on-state inwhich a unidirectional current between the input terminals 11 and 12 isconducted. In this case, the controller 6 is preferably configured tocontrol the bidirectional switch 2 so that the bidirectional switch 2 isin a reverse on-state from the second time point t2 to the third timepoint t3 between the second time point t2 and the end point of the halfcycle. The “reverse on-state” is a unidirectional on-state in which thebidirectional switch 2 allows an electric current to flow from an inputterminal of the input terminals 11 and 12 on a low potential side of theAC power supply 8 to an input terminal of the input terminals 11 and 12on a high potential side of the AC power supply 8. With theconfiguration, the occurrence of the reverse polarity voltage issuppressed from the second time point t2 to the third time point t3,thereby enabling reducing errors in detection by the phase detector 3caused by the reverse polarity voltage.

As stated in the present embodiment, it is preferable that the powersupply 5 have the capacitive device C1. With the configuration, thepower supply 5 enables the capacitive device C1 to store electric powersupplied from the AC power supply 8 during a period of time during whichthe input terminals 11 and 12 do not conduct. The power supply 5 cantherefore secure control power for the controller 6 even during a periodof time during which the input terminals 11 and 12 conduct. Note thatthe power supply 5 having the capacitive device C1 is not indispensableto the configuration of the dimmer 1. The capacitive device C1 may beomitted as appropriate.

As stated in the present embodiment, it is also preferable that thefirst time be a constant length of time. With the configuration, thecontroller 6 need cause the bidirectional switch 2 to be in abidirectional off-state during a period of time (first time period T1)until the constant length of first time from a start point of each halfcycle (zero cross point) t0 elapses. The processing of the controller 6becomes easy in comparison with the cases where the length of the firsttime is varied.

Although the processing of the controller 6 becomes complicated, thelength of the first time may be different between the first time periodT1 in the positive half cycle and the first time period T1 in thenegative half cycle.

As stated in the present embodiment, it is preferable that the phasedetector 3 be configured to output a detection signal when detecting azero cross point of the AC voltage Vac. In this case, more preferablythe dimmer 1 further includes the mask processor 61 configured to, whenreceiving a detection signal from the phase detector 3, disable thedetection signal over a constant length of mask time. The mask processor61 in the embodiment is not indispensable to the configuration of thedimmer 1. The mask processor 61 may be omitted as appropriate.

As stated in the present embodiment, it is also preferable that thedimmer 1 further include the stopper 13 configured to stop the powersupply 5 producing the control power during the stop time period. Thestop time period is a period of time from which at least a period oftime during which the bidirectional switch 2 is in an off-state isexcluded. The stopper 13 in the embodiment is not indispensable to theconfiguration of the dimmer 1. The stopper 13 may be omitted asappropriate.

As stated in the present embodiment, it is also preferable that thebidirectional switch 2 include the switch devices Q1 and Q2 that areelectrically connected in series between the pair of input terminals 11and 12.

(1.6) Modified Examples (1.6.1) Modified Example 1

As shown in FIG. 4, a dimmer 1A as Modified Example 1 according toEmbodiment 1 is different in part corresponding to the bidirectionalswitch 2 from the dimmer 1 according to Embodiment 1. Hereinafter, likeelements are assigned the same reference numerals as depicted inEmbodiment 1, and explanation thereof is omitted as appropriate.

In the present modified example, a bidirectional switch 2A includes aswitch device Q3 having double gate structure. The switch device Q3 is,for example a semiconductor switch having the double gate structure(dual gates) using a wide band gap of semiconductor material such as GaN(gallium nitride). The bidirectional switch 2A further includes a pairof diodes D3 and D4 that are connected in anti-series between inputterminals 11 and 12. The diode D3 has a cathode that is connected to theinput terminal 11 and the diode D4 has a cathode that is connected tothe input terminal 12. Both the diodes D3 and D4 have respective anodesthat are electrically connected to ground (earth) of a power supply 5.With the present modified example, the pair of diodes D3 and D4 alongwith a pair of diodes D1 and D2 constitute a diode bridge.

With the configuration of the modified example, the bidirectional switch2A enables further reducing a conduction loss in comparison with thebidirectional switch 2.

(1.6.2) Modified Example 2

As shown in FIG. 5, a dimmer 1B as Modified Example 2 according toEmbodiment 1 differs from the dimmer 1 according to Embodiment 1 in thata controller 6B is configured to estimate a zero cross point of ACvoltage Vac after a half cycle or more based on one detection signal ofa zero cross point. A circuit configuration of the dimmer 1B is the sameas that of the dimmer 1 according to Embodiment 1. Hereinafter, likeelements are assigned the same reference numerals as depicted inEmbodiment 1, and explanation thereof is omitted as appropriate.

A phase detector 3 is configured to output a detection signal whendetecting a zero cross point of the AC voltage Vac, like Embodiment 1.

In the modified example, the controller 6B is configured to, based onthe frequency of the AC voltage Vac, whenever receiving a detectionsignal from the phase detector 3, estimate a zero cross point after ahalf cycle of the AC voltage Vac or more as a virtual zero cross pointto generate a virtual signal at timing of the virtual zero cross point.Specifically, as shown in FIG. 6, the controller 6 generates a firstvirtual signal Si1 at a point in time when stand-by time Tzccorresponding to one cycle of the AC voltage Vac from the reception of afirst detection signal ZC1 elapses. Similarly, the controller 6Bgenerates a second virtual signal Si2 at a point in time when thestand-by time Tzc corresponding to one cycle of the AC voltage Vac fromthe reception of a second detection signal ZC2 elapses. Here, thestand-by time Tzc is set to be slightly longer than one cycle of the ACvoltage Vac in order to prevent the first virtual signal Si1 from beinggenerated prior to a next first detection signal ZC1. The stand-by timeTzc is also set to be slightly longer than one cycle of the AC voltageVac in order to prevent the second virtual signal Si2 from beinggenerated prior to a next second detection signal ZC2.

The controller 6B obtains a logical sum of the first detection signalZC1 and the first virtual signal Si1 as a trigger signal for determiningthe control timing of a bidirectional switch 2. Similarly, thecontroller 6B obtains a logical sum of the second detection signal ZC2and the second virtual signal Si2 as a trigger signal for determiningthe control timing of the bidirectional switch 2. The controller 6B candetermine the control timing of the bidirectional switch 2 based on thevirtual signals as trigger signals generated at the virtual zero crosspoints in place of a detection signal from the phase detector 3 evenwhen the phase detector 3 fails to detect a zero cross point.

The controller 6B may be configured to estimate twice or more a virtualzero cross point with respect to one detection signal of the zero crosspoint. In this case, the controller 6B generates a virtual signalwhenever the stand-by time Tzc elapses from a point in time when adetection signal is received. Here, the length of the stand-by time Tzcmay be varied so that a first stand-by time Tzc is slightly longer thanone cycle of the AC voltage Vac and a second stand-by time Tzc is almostthe same as one cycle of the AC voltage Vac.

The stand-by time Tzc for generating a virtual signal may be set on thebasis of the half cycle of the AC voltage Vac as a standard. Examples ofthe standard may include a half cycle, three times the length of a halfcycle (i.e., 1.5 cycles), four times the length of a half cycle (i.e., 2cycles) or more besides on cycle. When the length of the stand-by timeTzc is set to odd times the length of the half cycle as a standard, thecontroller 6B generates a second virtual signal Si2 at a point in timewhen the stand-by time Tzc elapses based on a first detection signalZC1. In this case, the controller 6B also generates a first virtualsignal Si1 at a point in time when the stand-by time Tzc elapses basedon a second detection signal ZC2. The controller 6B may thereforeconfigured to generate first and second virtual signals Si1 and Si2 fromonly one of first and second detection signals ZC1 and ZC2.

With the configuration of the present modified example, the controller6B performs stable reverse phase control in phase with the cycle of theAC voltage Vac even when the phase detector 3 fails to detect a zerocross point due to the influence of random noise or the like, or evenwhen a zero cross point is shifted owing to an instantaneous drop of theAC voltage Vac.

(1.6.3) Other Modified Examples

Hereinafter, modified examples of Embodiment 1, exclusive of ModifiedExamples 1 and 2 described above will be detailed.

The dimmers of Embodiment 1 and Modified Examples 1 and 2 describedabove are not limited to a load 7 with (an) LED devices as a lightsource, but may be applied to a light source that is equipped with acapacitor input type circuit and has a high impedance and is lit by asmall electric current. Examples of this sort of light source include anorganic EL (Electroluminescence) device and the like. The devices may beapplied to loads 7 as various light sources such as discharge lamps.

The switch driver 9 is not indispensable to the configuration of thedimmer 1, but may be omitted as appropriate. When the switch driver 9 isomitted, the controller 6 directly drives the bidirectional switch 2.

The mask processor 61 needs to be configured to disable a detectionsignal over a constant length of mask time, but is not limited to theconfiguration integrally provided with the controller 6. That is, themask processor 61 may be integrally provided with, for example the phasedetector 3. In this case, the mask processor 61 stops the operation ofthe phase detector 3 over the mask time, and thereby the detectionsignal can be disabled. The mask processor 61 may be provided separatelyfrom the controller 6 and the phase detector 3.

The mask time need be time that is set in advance on the basis of a halfcycle of the AC voltage Vac, but is not limited to the time that isslightly shorter than twice the length of the half cycle (i.e., onecycle) as exemplified in Embodiment 1. For example, the mask time may betime slightly shorter than the half cycle, or time slightly shorter thanthree times the length of the half cycle (i.e., 1.5 cycles). The masktime may also be set on the basis of four times the length of the halfcycle (i.e., 2 cycles) or more.

Each of the switch devices Q1 and Q2 constituting the bidirectionalswitch 2 is not limited to an n-channel enhancement MOSFET, but may be,for example, IGBT (Insulated Gate Bipolar Transistor) or the like. Therectifying devices for the unidirectional on-states (diodes) in thebidirectional switch 2 are not limited to the body diodes of the switchdevices Q1 and Q2, but may be discrete diodes like Modified Example 1.The diodes may be built in a package identical to the switch devices Q1and Q2.

The first time need be a constant length of time, and the length thereofmay be set as appropriate. For example, when the first time period T1 isthe sum of a period of time from a start point of a half cycle (zerocross point) t0 to a detection point and a period of time from thedetection point to a point in time when a constant delay time therefromelapses, the delay time is not limited to 300 [μs], but is appropriatelyset in a range of 0 [μs] to 500 [μs].

The third time point t3 need be before an end point of the half cycle(zero cross point) t4, and the length of time from the third time pointt3 to the end point of the half cycle t4 may be set appropriately. Forexample, when the length of time from the detection point to the thirdtime point t3 is shorter by a constant specified time than the halfcycle, the specified time is not limited to 300 [μs], but isappropriately set in a range of 100 [μs] to 500 [μs].

The stop time period during which the stopper 13 electricallydisconnects the power supply 5 from the pair of input terminals 11 and12 need be a period of time from which at least a period of time duringwhich the bidirectional switch 2 is in a bidirectional off-state (firsttime period T1 or fourth time period T4) is excluded. Therefore, thestop time period is not limited to the period of time whose start andend points are a point in time between the first and second time pointst1 and t2 and the third time point t3, respectively, but for example,the start point of the stop time period may be the first time point t1or the end point of the stop time period may be before the third timepoint t3.

The stopper 13 needs to be configured to stop the power supply 5producing the control power during the stop time period. The stopper 13is therefore not limited to the configuration where the power supply 5producing the control power is stopped by disconnecting the power supply5 from at least one of the pair of input terminals 11 and 12, or bycontrolling the semiconductor switch device included in the power supply5. For example, the stopper 13 may be configured to stop the output ofthe power supply 5 (output of control power) to increase the inputimpedance of the power supply 5, thereby stopping the power supply 5producing the control power.

The diodes D1 and D2 in the present embodiment are not indispensable tothe configuration of the dimmer 1. The diodes D1 and D2 may be omittedas appropriate.

Embodiment 2

As shown in FIG. 7, a dimmer 1C according to the present embodimentdiffers from the dimmer 1 according to Embodiment 1 in that it furtherincludes a voltage detector 53 configured to detect (measure) voltage ofcontrol power (voltage across capacitive device C1). Hereinafter, likeelements are assigned the same reference numerals as depicted inEmbodiment 1, and explanation thereof is omitted as appropriate.

In the present embodiment, first time is not a constant length of time,but time from a start point of a half cycle of AC voltage Vac (zerocross point) t0 to a point in time when voltage detected with thevoltage detector 53 (voltage across capacitive device C1) reaches aprescribed threshold. That is, the first time in the embodiment is not afixed length of time but a variable length of time that varies accordingto a detection value by the voltage detector 53.

Specifically, a power supply 5C is provide with the voltage detector 53.The voltage detector 53 is configured to detect voltage across thecapacitive device C1 of the power supply 5C to provide a detection valueto a controller 6C. The controller 6C is configured to, after receivinga detection signal from a phase detector 3, compare the detection valuefrom the voltage detector 53 with the prescribed threshold and determinethat a point in time when the detection value reaches the threshold is apoint in time when the first time elapses (i.e., first time point t1).Here, the threshold is set to voltage across the capacitive device C1when the capacitive device C1 has been charged such that the operationof the controller 6C until at least an end point of the half cycle ofthe AC voltage Vac (zero cross point) t4 can be secured

As explained above, the dimmer 1C according to the present embodimentfurther includes the voltage detector 53 configured to detect voltage ofcontrol power, and the first time is the time from a start point of ahalf cycle to a point in time when voltage detected with the voltagedetector 53 reaches the prescribed threshold. With the embodiment, thecontroller 6C can cause a bidirectional switch 2 to be in abidirectional on-state at a point in time when the capacitive device C1is charged such that requisite control power for the operation of thecontroller 6C can be secured. The dimmer 1C according to the embodimenttherefore enables shortening, to the utmost, the time from the startpoint of the half cycle of the AC voltage Vac (zero cross point) t0 to apoint in time when input terminals 11 and 12 conduct while securing therequisite control power for the operation of the controller 6C. Thecapacitive device C1 may be parasitic capacitance. In this case, theconfiguration has no discrete capacitive device.

The other configurations and functions are the same as those ofEmbodiment 1. The configuration of the present embodiment may be appliedby being combined with each configuration explained in Embodiment 1(including modified examples).

Other Embodiments

Embodiment 1 (including modified examples) and Embodiment 2 as describedabove secure the supply of electric power from the AC power supply 8 tothe power supply 5 over before and after a start point of a half cycleof the AC voltage Vac (zero cross point) t0 (first time period T1 orfourth time period T4), but are not limited to this.

The supply of electric power from the AC power supply 8 to the powersupply 5 may be secured during constant time only after the start pointof the half cycle of the AC voltage Vac (zero cross point) t0 (firsttime period T1). The supply of electric power from the AC power supply 8to the power supply 5 may also be secured during constant time onlybefore the start point of the half cycle of the AC voltage Vac (zerocross point) t0 (fourth time period T4). In these cases, the first orfourth time period T1 or T4 is set with the supply of electric powerfrom the AC power supply 8 to the power supply 5 secured preferentially.There is therefore an occasion in which a second time period T2 duringwhich electric power is supplied to a load 7 according to a dimminglevel received through an input device 4 is not set. An example of theoccasion includes a user's operation through an operation device, bywhich the light output of the load 7 is set to be maximum.

The abovementioned constant time is set so that enough supply ofelectric power from the AC power supply 8 to the power supply 5 isperformed, thereby enabling the suppression of the distortion of currentwaveform and a stable operation of a controller 6.

REFERENCE SIGNS LIST

-   1, 1A, 1B, 1C Dimmer-   2, 2A Bidirectional Switch-   3 Phase Detector-   4 Input Device-   5, 5C Power Supply-   6, 6B, 6C Controller-   7 Load-   8 AC Power Supply-   11 Input Terminal-   12 Input Terminal-   13 Stopper-   53 Voltage Detector-   61 Mask Processor-   C1 Capacitive Device-   Q1 Switch Device-   Q2 Switch Device-   Q3 Switch Device-   t0 Start point of half cycle (zero cross point)-   t1 First time point-   t2 Second time point-   t3 Third time point-   t4 End point of half cycle (zero cross point)-   Vac AC voltage-   ZC1 First detection signal-   ZC2 Second detection signal

The invention claimed is:
 1. A dimmer, comprising: a pair of inputterminals that is electrically connected in series between a loadconfigured to be lit and an AC power supply; a bidirectional switch thatis configured to be switched so as to conduct and interrupt abidirectional current between the pair of input terminals; an inputdevice that is configured to receive a dimming level representing avalue of light output of the load; and a controller configured tocontrol the bidirectional switch according to the dimming level, thecontroller controlling the bidirectional switch to keep thebidirectional switch in an off-state at a start point of a half cycle ofan AC voltage of the AC power supply, the controller controlling thebidirectional switch to turn the bidirectional switch to an on-state ata first time point when a first time period elapses from the startpoint, the controller also controlling the bidirectional switch to turnthe bidirectional switch to the off-state at a second time point when asecond time period elapses from the first time point, the controllerfurther controlling the bidirectional switch to keep the bidirectionalswitch in the off-state at an end point of the half cycle.
 2. The dimmerof claim 1, further comprising: a phase detector that is configured todetect a phase of AC voltage of the AC power supply; and a power supplythat is electrically connected between the pair of input terminals andconfigured to receive electric power from the AC power supply to producecontrol power, wherein the controller is configured to receive thecontrol power from the power supply to be activated, the controllerbeing configured to control the bidirectional switch based on adetection signal from the phase detector.
 3. The dimmer of claim 2,further comprising a voltage detector configured to detect voltage ofthe control power, wherein the first time period is time from the startpoint of the half cycle to a point in time when the voltage detectedwith the voltage detector reaches a prescribed threshold.
 4. The dimmerof claim 2, wherein the power supply has a capacitive device.
 5. Thedimmer of claim 2, wherein the dimmer further comprises a mask processorconfigured to disable a detection signal over a constant length of masktime when receiving the detection signal from the phase detector.
 6. Thedimmer of claim 2, further comprising a stopper configured to stop thepower supply producing the control power during a stop time period, thestop time period being a period of time from which at least a period oftime during which the bidirectional switch is in the off-state isexcluded.
 7. The dimmer of claim 2, wherein the phase detector isconfigured to output the detection signal when detecting a zero crosspoint of the AC voltage, and the controller is configured to estimate azero cross point of the AC voltage after the half cycle or more based onone detection signal.
 8. The dimmer of claim 2, wherein the period fromthe second time point to the end point of the half cycle includes athird time period and a fourth time period, and the controller isconfigured to cause the power supply to generate the control powerduring the first time period and the fourth time period.
 9. The dimmerof claim 8, wherein the first time period is a constant length of time.10. The dimmer of claim 8, further comprising a voltage detectorconfigured to detect voltage of the control power, wherein the firsttime period is time from the start point of the half cycle to a point intime when the voltage detected with the voltage detector reaches aprescribed threshold.
 11. The dimmer of claim 8, wherein the powersupply has a capacitive device.
 12. The dimmer of claim 8, wherein thephase detector is configured to output the detection signal whendetecting a zero cross point of the AC voltage, and the dimmer furthercomprises a mask processor configured to disable a detection signal overa constant length of mask time when receiving the detection signal fromthe phase detector.
 13. The dimmer of claim 8, further comprising astopper configured to stop the power supply producing the control powerduring a stop time period, the stop time period being a period of timefrom which at least a period of time during which the bidirectionalswitch is in the off-state is excluded.
 14. The dimmer of claim 1,wherein the first time period is a constant length of time.
 15. Thedimmer of claim 1, wherein the bidirectional switch includes two switchdevices that are electrically connected in series between the pair ofinput terminals.
 16. The dimmer of claim 1, wherein the bidirectionalswitch includes a switch device having double gate structure.
 17. Thedimmer of claim 1, wherein the second time period is longer than thefirst time period.
 18. The dimmer of claim 1, wherein the controllercontrols the bidirectional switch to keep the bidirectional switch inthe off-state from the start point of the half cycle to the first point,the controller controls the bidirectional switch to keep thebidirectional switch in the off-state from the second time point to theend point of the half cycle.
 19. A dimmer, comprising: a pair of inputterminals that is electrically connected in series between a loadconfigured to be lit and an AC power supply; a bidirectional switch thatis configured to be switched so as to conduct and interrupt abidirectional current between the pair of input terminals; an inputdevice that is configured to receive a dimming level representing avalue of light output of the load; and a controller configured tocontrol the bidirectional switch according to the dimming level, thecontroller controlling the bidirectional switch to turn thebidirectional switch to an off-state at a second time point when a firsttime period and a second time period elapse from a start point of a halfcycle of an AC voltage of the AC power supply, the controllercontrolling the bidirectional switch to turn the bidirectional switch toan on-state at a first time point when a first time period elapses froma start point of a next half cycle of the AC voltage.
 20. The dimmer ofclaim 19, wherein the controller controls the bidirectional switch tokeep the bidirectional switch in the off-state from the second timepoint of the half cycle to the first time point of the next half cycle.